1. Field of the Invention
The present invention relates to an apparatus for elastically supporting a power plant by a vehicle frame member such as a side member of a vehicle.
2. Description of the Related Art
As shown in FIGS. 7 to 9, the conventional power plant mounting apparatus for a vehicle is configured in a manner that a power plant 1, in which an engine and a transmission are integrally coupled to each other and laid horizontally, is supported on a vehicle body at three points, that is, at a mount member 3, at a mount member 5 and at a roll rod mount member 7. The power plant mounting apparatus is configured by the mount member 3 provided between the upper portion of the power plant 1 and a left side member 2 which extends in the longitudinal direction of the vehicle and has a closed section, the mount member 5 provided between the upper portion of the power plant 1 and a right side member 4 which extends in the longitudinal direction of the vehicle and has a closed section, and the roll rod mount member 7 provided so as to straddle between the lower portion of the power plant 1 and a chassis cross member 6 extending in a direction perpendicular to the longitudinal direction of the vehicle, that is, a vehicle width direction.
The mount member 3 includes a mount bracket 10 having an almost U-shaped section. A bottom portion of the mount bracket 10 is fixed to an inner side surface of the left side member 2. Both tip ends of the mount bracket 10 protrude in the vehicle width direction. The mount member 3 further includes an inner tube 12 and an outer tube 13 between which an insulator 11 formed by rubber-like elastic member is provided, and a bolt 14 having both ends that are respectively engaged with the both tip ends of the mount bracket 10 in a state that the bolt penetrates through the inner tube 12 and extends in the longitudinal direction of the vehicle. An arm 15 of the outer tube 13 is secured to the upper portion of the power plant 1 by means of bolts.
The mount member 5 is configured by a not-shown inner tube and an outer tube 16 between which an insulator formed by rubber-like elastic member is provided, and a not-shown bolt which is fixed to the upper portion of the power plant 1 via an arm 17 in a state that the bolt penetrates through the inner tube and extends vertically. The outer tube 16 is secured to the upper portion of the right side member 4 by means of a bolt.
The roll rod mount member 7 includes a two-branched mount bracket 18 fixed to the chassis cross member 6. Both tip ends of the bracket 18 protrude in the forward direction of the vehicle. The roll rod mount member 7 further includes a rod 20 one end of which is coupled to the bottom portion of the power plant 1 and the other end of which is integrally formed with an outer tube 19, an insulator 21 formed by rubber-like elastic member and provided between a not-shown inner tube and the outer tube 19, and a bolt 22 having both ends that are respectively engaged with the both tip ends of the mount bracket 18 in a state that the bolt penetrates through the inner tube and extends in the vehicle width direction. The power plant 1 is pivotally supported at three points on the vehicle body by means of the mount member 3, the mount member 5 and the roll rod mount member 7.
However, in the mount member 3, the shaft center of the bolt 14, which acts as the point of action of a load at the time of transmitting a vibratory force of the power plant 1 and an inertial force of the power plant 1 caused by accelerating or decelerating the running of the vehicle or by the steering operation and transmitted from the power plant 1 side to the left side member 2 side, is made largely offset by a distance d in the vehicle width direction from the sectional center point Q of the left side member 2. Thus, the supporting rigidity of the mount member 3 for supporting the power plant 1 is degraded, and the vibration damping characteristics of the mount member 3 is not enough. Since a relatively large space is required between the power plant 1 and the left side member 2, a position for disposing the mount member 3 within the engine compartment that is already narrow may be limited.
Also, at the time of rapid acceleration of a vehicle, a roll input force as a reaction force of the wheels acts on the power plant 1 as shown by an arrow A in FIG. 9. The mount member 3 provided at the upper portion of the power plant 1 has a low rigidity along the axial direction (the longitudinal direction of the vehicle). Since a load is applied to the mount member 3 along the axial direction, it is difficult for the mount member 3 to surely support the roll input force. Further, the mount member 3 is required to be provided with stoppers 25, 25 formed by rubber-like elastic member in order to prevent the outer tube 13 from making metal-contact with the tip portion of the mount bracket 10, when the outer tube 13 of the mount member 3 inclines in the longitudinal direction of the vehicle due to the elastic deformation of the insulator 11 caused by the roll input force, etc.
Further, at the time of rapid deceleration of a vehicle, a roll input force directed in the direction opposite to the arrow A in FIG. 9 acts on the power plant 1 so that a disadvantage similar to that of the aforesaid case arises.
Furthermore, in order to make the mount member 3 effectively reduce the vibration and noise caused by the operation of the plant 1, the fixing position of the mount member 3 with respect to the left side member 2 is required to be set at the most suitable position for each kind of the power plant 1. Thus, it is required to prepare many kinds of the left side members 2 in each of which the fixing position of the mount member 3 is suitably changed in accordance with the kind of the power plant 1.
Incidentally, power plant mounting apparatuses described in JP-A-2000-120770 and JP-A-9-240291 are conventionally known.